When to plant Brussels sprouts in Seattle and Tacoma, WA

Start Brussels sprouts from seed indoors Jan 18 – Feb 1, then plant the young plants in the garden in Seattle and Tacoma Mar 15 – Apr 26.

Moderate Plant young plants (starts)

Why these dates

Seattle and Tacoma's typical last spring frost is March 2. In the west-side valleys, the soil is usually ready for Brussels sprouts around March 15.

West-side valleys. The Willamette Valley, Puget Sound and southern Oregon valleys. Long frost-free seasons, but soil stays cold and wet into May, so warm crops wait for warm soil, not just the last frost.

Difficulty: Moderate
Sun: Full sun
Spacing: 24 inches apart
Planting depth: Plant starts at the depth they grew in the pot
Frost: Handles light frost
First harvest: About 100 days after planting

Step by step

Start seeds indoors Jan 18 – Feb 1 in trays or small pots under a grow light or in your sunniest window. Or skip this step and buy young plants (starts) at a garden center.
Harden off the young plants: about a week before planting, set them outside for a few hours a day, a little longer each day.
Plant them in the garden Mar 15 – Apr 26, 24 inches apart. Plant starts at the depth they grew in the pot.
Water deeply once or twice a week rather than a little every day, and mulch once the soil is warm.
Harvest: Pick sprouts from the bottom of the stalk up once they're firm and about an inch across. Frost improves the flavor.

Varieties that do well here

Long Island Improved
Diablo
Churchill

Watch out for

Aphids cluster on the sprouts in late summer. Knock them off with a strong spray of water every few days.

A long-season crop picked in fall and winter, when frost sweetens the sprouts. West of the Cascades, plants keep producing well into winter.

Common questions

When is the last frost in Seattle and Tacoma, WA?

Typically March 2. In 9 years out of 10, frost is over by March 23. These are 1991–2020 NOAA climate normals for Seattle-Tacoma International Airport.

Is it too late to plant Brussels sprouts in Seattle and Tacoma?

The spring planting window runs through April 26. Later plantings tend to struggle in summer heat.

When should I start Brussels sprouts from seed indoors in Seattle and Tacoma?

January 18 to February 1, which is 8 to 6 weeks before the March 15 planting date. Or buy young plants at a garden center instead.